1. Field of the Invention
The present invention relates generally to telecommunications systems and methods for positioning a mobile terminal within a cellular network, and specifically to offering location services in parallel to other existing services.
2. Background and Objects of the Present Invention
Cellular telecommunications is one of the fastest growing and most demanding telecommunications applications ever. Today it represents a large and continuously increasing percentage of all new telephone subscriptions around the world. A standardization group, European Telecommunications Standards Institute (ETSI), was established in 1982 to formulate the specifications for the Global System for Mobile Communication (GSM) digital mobile cellular radio system.
With reference now to FIG. 1 of the drawings, there is illustrated a GSM Public Land Mobile Network (PLMN), such as cellular network 10, which in turn is composed of a plurality of areas 12, each with a Mobile Switching Center (MSC) 14 and an integrated Visitor Location Register (VLR) 16 therein. The MSC/VLR areas 12, in turn, include a plurality of Location Areas (LA) 18, which are defined as that part of a given MSC/VLR area 12 in which a mobile station (MS) (terminal) 20 may move freely without having to send update location information to the MSC/VLR area 12 that controls the LA 18. Each Location Area 18 is divided into a number of cells 22. Mobile Station (MS) 20 is the physical equipment, e.g., a car phone or other portable phone, used by mobile subscribers to communicate with the cellular network 10, each other, and users outside the subscribed network, both wireline and wireless.
The MSC 14 is in communication with at least one Base Station Controller (BSC) 23, which, in turn, is in contact with at least one Base Transceiver Station (BTS) 24. The BTS is the physical equipment, illustrated for simplicity as a radio tower, that provides radio coverage to the cell 22 for which it is responsible. It should be understood that the BSC 23 may be connected to several BTS's 24, and may be implemented as a stand-alone node or integrated with the MSC 14. In either event, the BSC 23 and BTS 24 components, as a whole, are generally referred to as a Base Station System (BSS) 25.
With further reference to FIG. 1, the PLMN Service Area or cellular network 10 includes a Home Location Register (HLR) 26, which is a database maintaining all subscriber information, e.g., user profiles, current location information, International Mobile Subscriber Identity (IMSI) numbers, and other administrative information, for subscribers registered within that PLMN 10. The HLR 26 may be co-located with a given MSC 14, integrated with the MSC 14, or alternatively can service multiple MSCs 14, the latter of which is illustrated in FIG. 1.
Determining the geographical position of an MS 20 within a cellular network 10 has recently become important for a wide range of applications. For example, location services (LCS) may be used by transport and taxi companies to determine the location of their vehicles. In addition, for emergency calls, e.g., 911 calls, the exact location of the mobile terminal 20 may be extremely important to the outcome of the emergency situation. Furthermore, LCS can be used to determine the location of a stolen car, for the detection of home zone calls, which are charged at a lower rate, for the detection of hot spots for micro cells, or for the subscriber to determine, for example, the nearest gas station, restaurant, or hospital, e.g., "Where am I" service.
Currently, when an MS 20 is being positioned, the MS 20 is not always able to make or receive calls, send or receive short messages, or activate other supplementary services. With reference now to FIG. 2 of the drawings, using the Open Systems Interconnection (OSI) model, which was developed by the International Standards Organization (ISO) in 1982, the inability of the MS 200 to engage in other activities while being positioned can be explained by describing the GSM system as several functional layers arranged in hierarchical form. These consist of the physical layer 205, the data link layer 210 and the application layer 215, which are on both the network side (MSC 240) and the terminal side (MS 200). The application layer 215 is composed of three sublayers: Radio Resource (RR) 220, Mobility Management (MM) 230 and Connection Management (CM) 235.
The CM protocol 235, which is the highest layer, controls three separate transaction types: end-to-end call control (CC layer) 232, short message handling delivery (SM layer) 234 and call independent handling of supplementary services (SS layer) 236. As it is today, it is possible for a mobile subscriber to establish several CM-connections 230, using the same MM and RR-connection 220. Therefore, it is possible to provide several telecommunication services at one time and to change between different services if necessary.
Any transaction may be established in parallel to any combination of other transactions. However, for a given RR-connection 220, MM-connections 230 can only be established once for each of the transaction types 232, 234 and 236. Thus, only one MM-connection 230 is allowed at a time per transaction type 232, 234 and 236. That implies that, if LCS were to be defined as part of either the CC layer 232, SM layer 234 or SS layer 236, it would be impossible to offer an LCS transaction at the same time as another transaction if both transactions belonged to the same transaction type (CC 232, SS 234 or SM 236).
It is, therefore, an object of the present invention to allow LCS transactions to be performed in parallel to other existing transactions such as mobile originating call or mobile terminating call, supplementary services and mobile originating or mobile terminating short messages.